The need for compression to facilitate recording of a digital video signal on relatively narrow-band media, such as a compact disc (CD), has been recognized. In a system proposed by Takahashi et al. in U.S. Pat. No. 4,520,401, a digital video signal is encoded using differential pulse code modulation (DPCM) for recording on a digital audio disc. In the known system, luminance (Y) and chrominance (R-Y, B-Y) components of a video frame are separately compressed using DPCM. A circuit divides the components into picture element data groups of a specific number of rows or columns which are adjacent on a screen. A header signal is provided having a synchronizing signal, a picture mode identification signal and a picture information quantity identification code. The header signal is added to the beginning position of each of the divided picture element data groups to produce a digital video output signal having a signal format in which the digital luminance, the two kinds of digital color difference signal and the header signal are time sequentially multiplexed and recorded.
In an example of the Takahashi et al. system still frames of digital video are recorded and updated at a rate of about four seconds per frame. The division of the compressed data into groups of lines with each group containing complete color information provides a psuedo-motion effect in that the line groups may be sequentially updated while displaying the previous frame thereby providing a partially moving picture.
The system described in the parent application Ser. No. 07/408,085 is directed to meeting the need for providing a compressed digital video signal representative of a full motion color video signal, which is suitable for recording or transmission using relatively narrow band media; and for decoding such a compressed signal to enable display of full motion video images at normal video frame rates. Although that system is effective for encoding and decoding most images, it was discovered that the system had some difficulty with certain images such as, for example, images containing a large amount of fast and/or uncoordinated motion; that is, motion which does not occur substantially uniformly in the same direction over relatively large portions of the image. It was found that such images were difficult to encode since the linear fill technique employed by the system was too gross an encoding method to be used with images containing substantial amounts of uncoordinated moving detail. With such images, it is desirable to encode each individual pixel; however, the system disclosed in the parent application is often allowed only an average of one-half bit for encoding each pixel. Therefore, it is desirable to add a feature to that system which will enable effective compression and decompression of selected images such as those having a substantial amount of moving detail.